It is known that cellular plastics may be obtained from mixtures of unsaturated and saturated polyester resins, styrene, diisocyanates and organic peroxides (see, e.g. U.S. Pat. No. 2,642,403). The polyesters used are of high molecular weight and are either highly viscous or solid resins. The disadvantage of using resins of this type is that little or no filler may be used. The polyester resins used only contain small proportions of hydroxyl groups which only allow the formation of small proportions of urethane bonds in the cellular plastics. Accordingly, another disadvantage is the low crosslink density. The low crosslink density is responsible for the poor heat resistance and the inadequate resistance to chemicals and solvents of the cellular plastics.
Solutions containing polyhydroxy compounds, polyisocyanates and polymerizable vinyl compounds, as solvents, may also be used for the production of coatings, lacquers and bonds (see e.g. German Pat. No. 951,729). As disclosed in German Pat. No. 956,720, the same solvents are also recommended for the production of moldings, including foam moldings. The disadvantages referred to above apply fully to those applications. Another disadvantage of the solutions noted above is the fact that, in some cases, the polyhydroxy compounds are completely free from unsaturated compounds, with the result that the polymerizable vinyl compounds are unable to enter into any copolymerization reactions.
The use of conventional unsaturated polyesters, vinyl compounds and the addition of isocyanates has been described in German Pat. No. 963,019, and French Pat. Nos. 1,107,741 and 1,130,293. The disadvantages referred to above apply equally to these products.
It is also known that unsaturated polyesters may be reacted with isocyanates before copolymerization with vinyl compounds (see e.g. German Patent 895,529). The disadvantage of this process is that the urethane-modified polyesters have an even higher viscosity than conventional unsaturated polyester.
In another process for the production of foams from high molecular weight polyurethanes (German Pat. No. 945,479), unsaturated, linear or branched polyesters completely or predominantly containing terminal carboxyl groups and polymerizable vinyl or alkyl compounds are reacted with polyisocyanates in the presence of polymerization accelerators. One disadvantage of this process is that the polyesters containing terminal carboxyl groups are solid or highly viscous substances. Another disadvantage is the fact that it is only possible to produce foams by this process.